This invention relates to data communication systems, and more particularly, to a method and mechanism for processing high and low priority data packets to be transmitted by a communication switch.
A multiport communication switch may be provided in a data communication network to enable data communication between multiple network stations connected to various ports of the switch. A logical connection may be created between receive ports and transmit ports of the switch to forward received data packets, e.g., frame data, to appropriate destinations. Based on frame headers, a frame forwarding arrangement selectively transfers received frame data to a destination station.
Frame data received at a receive port of the communication switch are transferred to an external memory and subsequently retrieved and transmitted from a respective transmit port of the switch. Some frame data are assigned as high priority data and others are assigned as low priority data. Since all high priority frame data should be transmitted from a respective transmit port before any low priority frame data is transmitted from that port, there is a need to provide a mechanism to assure that this occurs.
The invention provides a novel arrangement for transmitting, from a respective transmit port of a multiport communication switch, all data packets which are of high priority before transmitting any data packet of low priority. The arrangement includes a multiport data communication system for switching data packets between ports and includes a plurality of receive ports for receiving data packets, a plurality of transmit ports for transmitting data packets, circuitry for deciding whether each received data packet is one of high priority and low priority, a memory storing each received data packet, and transferring circuitry transferring, from the memory to a respective transmit port, all data packets of high priority corresponding to the transmit port prior to transferring any data packet of low priority corresponding to the transmit port.
In one aspect of the invention, the transferring circuitry includes a transmit queue for each transmit port and all data packets of high priority are transferred from the memory and placed in the transmit queue for each transmit port prior to any data packet of low priority.
In another aspect of the invention, a memory location designator is provided for each data packet indicating where the corresponding data packet is stored in the memory and a plurality of queuing devices are provided corresponding to the plurality of transmit ports. Each queuing device has a high priority queue queuing memory location designators corresponding to data packets of high priority to be transmitting by the respective transmit port and a low priority queue queuing memory location designators corresponding to data packets of low priority to be transmitting by the respective transmit port.
In still another aspect of the invention, the transferring circuitry further includes logic circuitry corresponding to each transmit queue, the logic circuitry determining whether the low priority queue of a respective queuing device has a memory location designator for a data packet to be retrieved from the memory and sent to the corresponding transmit queue only when the high priority queue of said respective queuing device is empty of memory location designators.
The invention also provides a novel method of processing received data packets for transfer to the plurality of transmit ports of a multiport communication system having a plurality of receive ports for receiving data packets and a plurality of transmit ports for transmitting data packets. The method comprises, for each received data packet, deciding whether each received data packet is one of high priority and low priority, transferring the received data packets to a memory, and for each transmit port, transferring data packets from the memory to each transmit port which are of high priority prior to transferring any data packet from the memory to each transmit port which is of low priority.
The communication system has a plurality of queuing devices and a plurality of transmit queues each corresponding to the plurality of transmit ports, and each queuing device has a high priority queue and a low priority queue. The method further comprises transferring the received data packets to the memory at a location indicated by a memory location indicator, and based on a result of the deciding, storing each memory location indicator in one of the high priority queue and low priority queue corresponding to each transmit port, and for each respective transmit port, transferring from the memory to the corresponding transmit queue all data packets corresponding to memory location indicators in the high priority queue of the respective queuing device prior to transferring from the memory to the corresponding transmit queue any data packet corresponding to a memory location indicator in the low priority queue of the respective queuing device.
Various objects and features of the present invention will become more readily apparent to those skilled in the art from the following description of a specific embodiment thereof, especially when taken in conjunction with the accompanying drawings.